Sorghum Anthracnose Research Articles

In vitro antimicrobial activity of aqueous extracts from Lentinula edodes isolates against Colletotrichum sublineolum and Xanthomonas axonopodis pv. Passiflorae

The aim of this study was to evaluate the antimicrobial activity of aqueous extracts from fruiting bodies of different isolates of Lentinula edodeson the pathogens Colletotrichum sublineolum, the causal agent of anthracnose in sorghum, and Xanthomonas axonopodispv. passiflorae, the causal agent of bacterial spot in passion fruit. Results showed that the aqueous extracts from isolates LE JAB-K and LE 95/01 significantly reduced C. sublineolumspore germination,while the isolate LE 96/22 was the only one to inhibit the pathogen mycelial growth. However, all L. edodesisolates showed inhibitory effect on C. sublineolumappressorium formation. Regarding X. axonopodispv. passiflorae, the aqueous extracts from all L. edodesisolates significantly reduced the in vitromultiplication of the bacterium. However, antimicrobial activity was lost when the extracts were autoclaved, demonstrating their thermolabile property. The aqueous extract from isolate LE 96/22 was also partially purified by anion exchange chromatography and fraction V exhibited high inhibitory activity on the in vitromycelial growth of C. sublineolum, while the multiplication of X. axonopodispv. passifloraewas inhibited by fractions IV, V and VII. Thus, L. edodesisolates were shown to produce compounds exhibiting antifungal and antibacterial activities against phytopathogens, which are mainly concentrated in fraction V.

Pathotypes of Colletotrichum sublineolum in Response to Sorghum Populations with Different Levels of Genetic Diversity in Sete Lagoas‐MG

AbstractSorghum anthracnose is one of the most important and destructive diseases of sorghum. Genetic resistance has been the most efficient strategy to control the disease, but the high variability of the pathogen population in Brazil has resulted in only modest efficacy. Accordingly, we investigated the variability of Colletotrichum sublineolum in response to sorghum populations with three levels of genetic diversity: pure stand, three‐way hybrids and physical mixtures of three‐way hybrids. Six plots of each treatment were planted in different areas and at different dates. A total of 480 isolates, that is 40 single‐conidium isolates per plot, were collected from the field experiment to characterize the variability of the pathogen in each host population. Isolates were inoculated in a greenhouse on a differential line set composed of eight sorghum inbred lines. Our results reveal that the pathogen populations derived from three‐way combinations had higher pathotype diversity than did those derived from pure stand host populations. More complexly, virulent phenotypes were also developed in genetically diverse stands compared to pure stand host populations. The diversification of the host population limits pathogen adaptation, thus resulting in a significantly higher number of pathotypes. The results of this study will improve the management of sorghum anthracnose in the field by helping sorghum breeders maintain disease resistance.

Genotype rotation for leaf anthracnose disease management in sorghum

The aim of this study was to evaluate the use of genotype rotation as a sustainable management strategy for the control of foliar anthracnose of sorghum. Three grain sorghum hybrids, one susceptible (BR 304) and two resistant to anthracnose (1G150 and DAS740) were tested in continuous planting and genotype rotation during seven growing seasons. The area under disease progress curve (AUDPC) of sorghum anthracnose severity was significantly lower in the genotype rotation than in the continuous planting. The disease severity in the susceptible genotype BR 304 in rotation with the resistant genotypes 1G150 or DAS740 decreased about 42% and 70% respectively, compared to its continuous planting. A significant reduction of leaf blight disease severity caused by Exserohilum turcicum in DAS740 planted rotated with BR 304 was also observed. The grain yields of the three genotypes were significantly higher in the rotation system compared to continuous planting. The genotype rotation can be considered a practical management strategy for reducing the impact of anthracnose and other diseases in sorghum.

Biological control of sorghum anthracnose with rhizosphere and rhizoplane fungal isolates from perennial grasses of the Western Ghats of India

Sorghum is an important drought tolerant crop cultivated for food and fodder purposes. Anthracnose disease caused by Colletotrichum graminicola is a major constraint in sorghum productivity in India. Certain antagonistic fungi, that were isolated in the previous study from the rhizosphere and rhizoplane of perennial grasses in India, were studied for their antagonism in vitro to C. graminicola, root colonization ability and rhizosphere competence. Out of 138 isolates tested, 89 were antagonistic. Fifteen fungal isolates with greater than 70 % in vitro inhibition zone to the pathogen tested positive for root and rhizosphere colonization abilities. Three isolates – Chaetomium globosum isolate 57, Trichoderma harzianum isolate 184 and Fusarium oxysporum (NSF isolate 9) with prominent biocontrol potentials were tested for the control of sorghum anthracnose in greenhouse and field. Chaetomium globosum, Trichoderma harzianum and Fusarium oxysporum isolates decreased seedling mortality, and incidence and severity of disease at different growing stages. They promoted plant growth (dry biomass- 45.3, 40.0 and 46.7 %) and increased yield (grain biomass- 33.3, 23.8 and 49.2 %) respectively, over control in field. The population of the above fungi in soil was moderately high at harvest stage. The present investigation revealed that fungal isolates from rhizosphere and rhizoplane of perennial grasses could be employed to manage anthracnose and enhance plant growth and yield potentialities in sorghum, at the same time.

Identification of genetic markers linked to anthracnose resistance in sorghum using association analysis

Anthracnose in sorghum caused by Colletotrichum sublineolum is one of the most destructive diseases affecting sorghum production under warm and humid conditions. Markers and genes linked to resistance to the disease are important for plant breeding. Using 14,739 SNP markers, we have mapped eight loci linked to resistance in sorghum through association analysis of a sorghum mini-core collection consisting of 242 diverse accessions evaluated for anthracnose resistance for 2 years in the field. The mini-core was representative of the International Crops Research Institute for the Semi-Arid Tropics' world-wide sorghum landrace collection. Eight marker loci were associated with anthracnose resistance in both years. Except locus 8, disease resistance-related genes were found in all loci based on their physical distance from linked SNP markers. These include two NB-ARC class of R genes on chromosome 10 that were partially homologous to the rice blast resistance gene Pib, two hypersensitive response-related genes: autophagy-related protein 3 on chromosome 1 and 4 harpin-induced 1 (Hin1) homologs on chromosome 8, a RAV transcription factor that is also part of R gene pathway, an oxysterol-binding protein that functions in the non-specific host resistance, and homologs of menthone:neomenthol reductase (MNR) that catalyzes a menthone reduction to produce the antimicrobial neomenthol. These genes and markers may be developed into molecular tools for genetic improvement of anthracnose resistance in sorghum.

Management of sorghum anthracnose through diversification of genetic resistance in host population

The aims of the present study were to assess the efficiency of hybrid sorghum mixtures for the management of anthracnose and analyze the virulence diversity and structure in the pathogen populations developed in response to these mixtures. Proportions of 25%, 50% and 75% of the susceptible BRS304 hybrid in relation to the resistant IG150 hybrid were evaluated. Six weekly evaluations of severity were performed. The data were transformed into area under disease progress curve (AUDPC). The isolates of Colletotrichum sublineolum were sampled from hybrid mixtures cultivated in Sete Lagoas and Indianopolis (Brazil) as well as sorghum fields in Rio Verde and Parauna (Brazil). The increase in the proportion of the resistant hybrid in the mixtures led to a reduction in anthracnose severity. The most effective proportions were those with 25% and 50% of the susceptible variety blended with the resistant variety. Complex breeds of C. sublineolum predominated in the populations and a reduction in phenotype diversity was observed. This reduction in diversity was attributed to deviations in the degree of polymorphism in relation to virulence. However, the increase in complex breeds did not imply lesser efficiency on the part of the resistant hybrid in conferring protection to the susceptible hybrid.

Silicon and Fungicide Effects on Anthracnose in Moderately Resistant and Susceptible Sorghum Lines

AbstractThis study aimed to evaluate the effect of silicon (Si) and its interaction with fungicide on the management of sorghum anthracnose. The experiments were carried out in Si‐deficient soil in the 2008/2009 and 2009/2010 growing seasons in a randomized, complete block, split‐split plot design with four replications. Calcium silicate (CS) and lime (L), at the rates of 6 and 5 ton/ha, respectively, were randomly assigned to the main plot. Two sorghum lines, BR‐008 (resistant) and BR‐009 (susceptible), were assigned to the split plots. The split‐split plots corresponded to with or without the fungicide Opera® (epoxiconazole + pyraclostrobin). The residual effect of CS and L from the 2008/2009 growing season was evaluated in the 2009/2010 growing season. For the 2008/2009 growing season, the area under anthracnose progress curve (AUAPC) was reduced by 39 and 42% for lines BR‐008 and BR‐009, respectively, with the application of CS. In the presence of the fungicide, the AUAPC was reduced by 35 and 42% for the CS and L treatments, respectively. Calcium silicate with and without fungicide contributed to decreasing the AUAPC by 44 and 37%, respectively. The fungicide spray decreased the AUAPC by 50 and 39% for lines BR‐008 and BR‐009, respectively. Without fungicide, the AUAPC decreased by 88% for line BR‐008 compared with line BR‐009; however, with fungicide, the reduction reached 90%. The Si leaf tissue concentration significantly increased with the CS application (5.9 g/kg) compared with the L application (0.3 g/kg), regardless of the sorghum line. The yield increased by 0.6 ton/ha with the CS compared to the L application. The fungicide increased yield by 0.48 ton/ha compared with the non‐fungicide spray treatment. The residual effect of CS in the soil increased Si leaf tissue concentration and yield as well as reduced the intensity of anthracnose in the 2009/2010 growing season.

Utilização de multilinhas dinâmicas para o manejo da antracnose do sorgo

O objetivo deste trabalho foi avaliar a eficiência do uso de multilinhas dinâmicas, por meio de misturas genéticas em populações de híbridos triplos, no manejo da antracnose do sorgo, causada pelo fungo Colletotrichum sublineolum. Foram obtidos 18 híbridos triplos a partir de sete linhagens que continham genes distintos para resistência à doença. Os 25 genótipos de híbridos e linhagens foram avaliados em campo. Verificou-se, em alguns híbridos, grau de resistência superior ao observado para a linhagem mais resistente utilizada nos cruzamentos, o que indica efeito aditivo dos genes de resistência das diferentes linhagens na composição da resistência final dos híbridos. O usodas multilinhas dinâmicas reduziu a intensidade da doença no campo e aumentou a produtividade. Essa estratégia torna possível a utilização de linhagens que apresentam características agronômicas desejáveis, mas são suscetíveis à antracnose.

Two loci in sorghum with NB-LRR encoding genes confer resistance to Colletotrichum sublineolum

The aim of this work was to identify plant resistance genes to the sorghum anthracnose fungus Colletotrichum sublineolum. cDNA-AFLP transcript profiling on two contrasting sorghum genotypes inoculated with C. sublineolum generated about 3,000 informative fragments. In a final set of 126 sequenced genes, 15 were identified as biotic stress related. Seven of the plant-derived genes were selected for functional analysis using a Brome mosaic virus-based virus-induced gene silencing (VIGS) system followed by fungal inoculation and quantitative real-time PCR analysis. The candidate set comprised genes encoding resistance proteins (Cs1A, Cs2A), a lipid transfer protein (SbLTP1), a zinc finger-like transcription factor (SbZnTF1), a rice defensin-like homolog (SbDEFL1), a cell death related protein (SbCDL1), and an unknown gene harboring a casein kinase 2-like domain (SbCK2). Our results demonstrate that down-regulation of Cs1A, Cs2A, SbLTP1, SbZnF1 and SbCD1 via VIGS, significantly compromised the resistance response while milder effects were observed with SbDEFL1 and SbCK2. Expanded genome analysis revealed that Cs1A and Cs2A genes are located in two different loci on chromosome 9 closely linked with duplicated genes Cs1B and Cs2B, respectively. The nucleotide binding-leucine rich repeat (NB-LRR) encoding Cs gene sequence information is presently employed in regional breeding programs.

Anthracnose field evaluation of sorghum germplasm from Botswana

Sorghum anthracnose is a disease of worldwide importance and host-plant resistance is the most practical method of disease management. In this study, 154 sorghum accessions from the Botswana collection maintained by the United States National Plant Germplasm System were inoculated with Colletotrichum sublineolum and evaluated for disease resistance at the Tropical Agriculture Research Station in Isabela, Puerto Rico during 2007 and 2008. A resistant response was observed for 69 accessions in 2007 and for 48 accessions in 2008 with no acervuli development observed on inoculated leaves. The low frequency of resistant germplasm is expected from a region of low annual rainfall. However, disease severity was low for the susceptible accessions with a mean severity of 11% for the 85 susceptible accessions observed in 2007 and 17% for the 106 susceptible accessions identified in 2008. The highest frequency of resistant accessions was observed for the Ngamiland district with 58% of the accessions rated as resistant, whereas the frequency of resistant accessions ranged from 22% to 36% for the other districts. The lowest mean disease severity was also observed for the susceptible accessions from the Ngamiland district with the highest mean disease severity observed for susceptible accessions from the Kgatleng district. The resistant accessions identified in this study would be useful for the development of disease resistant varieties and the results indicated an ecogeographic association with disease resistance.

Incidence and Severity of Sorghum Anthracnose in Ethiopia

A two year survey was conducted to determine incidence and severity of sorghum anthracnose in different sorghum growing regions in Ethiopia. A total of 487 fields in 49 districts were surveyed in each of the 2005 and 2007 production season. Incidence of sorghum anthracnose was assessed as the percentage of plants with visible symptoms in a field and anthracnose severity was evaluated as the percentage of leaf area with symptoms. Also, the relationship of the incidence and severity of the disease to the altitude of the fields and weather conditions were determined. Results from the 2 years survey revealed that sorghum anthracnose is present in most (84%) of the survey districts. However, both incidence and severity of the disease varied significantly (p<0.0001) among the survey areas. Anthracnose incidence ranged from 0 to 77% and severity of the disease varied between 0 and 59% on average for the two years. The two year average anthracnose severity classes ranged from trace (<5%) to severe (up to 59%) and the disease was generally more severe in the Southwest and South regions. However, some districts in the East and North Ethiopia also had fields with severe anthracnose infection. It was also found out that the prevailing weather conditions especially rainfall has a significant impact on both anthracnose incidence and severity.

Effect of Host Genotypes and Weather Variables on the Severity and Temporal Dynamics of Sorghum Anthracnose in Ethiopia

The severity and temporal dynamics of anthracnose on susceptible (BTx623 and AL70) and resistant lines (2001 PWColl No. 022 and 2001 HararghieColl No. 12) were studied in field plots during the 2007 and 2008 growing seasons in southern Ethiopia. The initial, final and mean anthracnose severities and area under disease progress curves were used as criteria to evaluate the response of the genotypes. Over the two years, the initial, final and mean anthracnose severities ranged from 0.88 to 16.13%, 7.56 to 78.38% and 3.57 to 46%, respectively, while area under disease progress curve averaged for the two years ranged from 221.31 to 2951.88. All the evaluation criteria showed highly significant variations (p<0.0001) among the genotypes and the Ethiopian genotype 2001 PWColl No. 022 consistently had the lowest disease levels regardless of the evaluation criteria and growing season. The disease appeared rather late and progressed slowly on this genotype. On the other hand, the exotic cultivar, BTx623, showed the most sever anthracnose infection. Initial anthracnose severity was significantly higher and the disease developed rapidly on BTx623 than on the other three genotypes. The other two genotypes showed intermediate response and progression of the disease. Correlation and regression analyses revealed a significantly strong association between rainfall and anthracnose severity but temperature appeared to have little/no impact on the development of anthracnose in the field. The present study confirmed the effect of both host genotypes and weather, particularly rain on anthracnose development. The Ethiopian sorghum genotype 2001 PWColl No. 022 was recommended as stable source of resistance against this important disease.

Evaluation of resistance in sorghum genotypes to the causal agent of anthracnose

The high degree of variability of the fungus Colletotrichum sublineolum, causal agent of sorghum anthracnose, has hindered the development of resistant hybrids. The objective of this research was to compare the aggressiveness of different fungal isolates and evaluate the genetic resistance (vertical and horizontal resistance) of various sorghum lines and hybrids. Twelve isolates, collected from different regions, were inoculated on 87 lines and 63 hybrids in the field and disease severity was evaluated. The diallel crossing method provided information about the vertical and horizontal resistance of the host, as well as the aggressiveness/ virulence of the pathogen. This genetical method was very promising for the identification of horizontal resistance in the sorghum- Colletotrichum sublineolum pathosystem, and for the prediction of anthracnose resistance in hybrids in the absence of vertical resistance. Dilatory resistance was detected in 14.94% of the inbred lines, and in 19.04% of the hybrids. Significant differences in aggressiveness and virulence of the isolates were also observed.

Development of Anthracnose on Grain Sorghum Hybrids Inoculated with Recently Described Pathotypes of Colletotrichum sublineolum Found in Arkansas.

Sorghum anthracnose, caused by Colletotrichum sublineolum, is found in most grain-sorghum-producing areas, including Arkansas. Yield losses can be severe in susceptible sorghum hybrids, suggesting that host resistance will continue to be critical for maintaining high yields. However, genetic control is often unsuccessful because of haplotype and pathotype variability within the C. sublineolum population. The objective of this research was to assess the levels of resistance of selected grain sorghum hybrids to isolates of the recently described pathotypes of C. sublineolum found in Arkansas. Field experiments were conducted in 2005 and 2006 to evaluate the reaction of 10 sorghum hybrids to eight C. sublineolum pathotypes by collecting anthracnose severity ratings at 7, 14, 21, and 28 days after inoculation. Based on these disease severity ratings, the area under the disease progress curve was calculated for each pathotype by hybrid interaction. These data showed that different levels of resistance are available in the current grain sorghum hybrids to different pathotypes. Cargill 888Y was resistant to all pathotypes in both years. However, Asgrow A571, DEKALB DKS53-11, FFR 318, and Pioneer 84G62 were moderately susceptible to susceptible to all pathotypes tested in both years. Pathotype 9 caused the most disease on 7 of the 10 hybrids evaluated in 2005 but, in 2006, pathotypes 12 and 13 surpassed pathotype 9 for disease severity on 9 of the 10 hybrids. More work is needed to assess host resistance and the effect of sorghum anthracnose on yield parameters of grain sorghum hybrids planted in Arkansas.

Field Assessment of Anthracnose Disease Response for the Sorghum Germplasm Collection from the Mopti Region

Problem statement: Sorghum anthracnose (Colletotrichum sublineolum) is a highly variable pathogen and new sources of host plant resistance are required for the development of resistant sorghum varieties. Germplasm collections are an important source of host plant resistance and screening germplasm will be essential to identify new sources of resistance. Approach: The sorghum (Sorghum bicolor) collection from the Mopti region of Mali was inoculated with Colletotrichum sublineolum and evaluated for foliar anthracnose disease response in Isabela, Puerto Rico during the 2004 and 2005 growing seasons using a partially balanced lattice design with three replications. Results: A resistant response was observed for 45 of the 97 accessions in the collection and mean infection severity for the 52 susceptible accessions was 27.6%. An association was observed between resistance and the administrative district where the germplasm was collected. More than 50% of the accessions from the Bandiagara and Bankass districts showed a resistant response. The lowest frequency of resistant germplasm was observed for the Mopti district with 25% of the accessions showing a resistant response. The susceptible accessions from the Mopti district, however, showed the lowest mean infection severity. Approximately 44% of the accessions from the Douentza district showed a resistant response with the susceptible accessions showing the highest mean infection severity. These results suggest an association between annual rainfall and anthracnose resistance, with sorghum accessions from drier regions showing greater susceptibility. Anthracnose resistance also showed an association with sorghum race classification and race guinea accessions were more frequently resistant as compared to accessions classified as race durra or durra-bicolor. Conclusion: The results indicated that anthracnose resistant sorghum germplasm is frequent in the Mopti region of Mali and that ecogeographic origin and sorghum characterization information can be used to aid in germplasm selection or germplasm acquisition to identify anthracnose resistant sources.

Evaluation of the biological control by the yeast Torulaspora globosa against Colletotrichum sublineolum in sorghum

The yeasts are microorganisms with great potential for biotechnological applications in diverse areas. The biological control of phytopathogens by yeasts has showed satisfactory results under laboratory conditions, and it has already produced commercial formulations. With this as focus, this work aims to perform in vitro and in vivo evaluations of the action of a Torulaspora globosa yeast strain (1S112), isolated from sugarcane rhizosphere, against the phytopathogenic mold Colletotrichum sublineolum, the causative agent of anthracnose in sorghum. In vitro experiments included the antagonism test in Petri dishes with morphological hyphal evaluation; yeast killer activity; siderophore, volatile compound and hydrolytic enzyme production. In vivo experiments were conducted in greenhouse conditions with a sorghum variety susceptible to C. sublineolum by evaluating the anthracnose disease for 6 weeks. The results indicated that the yeast strain significantly controlled the fungal growth, either in vitro or in vivo. The strain of T. globosa exhibited killer activity against two sensitive strains, which is a novel capacity for this species. The yeast did not produce siderophores, volatile compounds or hydrolytic enzymes, although it has reduced the mycelial growth, resulting in hyphal deformities but not cell death. The yeast controlled the anthracnose disease in sorghum, either inoculated before or after the fungal spores, suggesting that the competition for space and nutrients to dominate the mold and killer toxin production, altering the hyphal morphology, are mechanisms utilized by the yeast in the biocontrol.

Efficacy of seed treatment with Apron Star 42 WS and foliar application of emulsified neem ( Azadirachta indica , A. Juss) seed oil in the control of sorghum ( Sorghum bicolar L. Moench) anthracnose in the Sudan savanna of Nigeria

The efficacy of seed treatment with Apron Star 42WS followed by foliar application of emulsified neem seed oil in controlling sorghum anthracnose caused by Colletotrichum graminicola was evaluated during the 1999 and 2000 cropping seasons. The experiments were laid out in a strip plot design with three replications. The seed treatment formed the main plot factor while three application regimes of the emulsified neem seed oil were assigned to the sub-plots. The results showed that seed treatment with Apron Star 42WS supplemented with foliar sprays of emulsified neem seed oil significantly reduced the incidence and severity of anthracnose compared to the untreated crops in both seasons. At maturity (120 DAS), the combined disease incidence was 22.25% and 33.45% in the treated and untreated crops, respectively, while disease severity for the same period was 17.63% and 26.08% for the treated and untreated crops, respectively. Also three sprays with the emulsified neem seed oil gave significantly lower disease incidence and severity (23.21% and 18.87%, respectively) compared to one spray (26.34% and 20.07%, respectively) and the control (31.95% and 25.54%, respectively). The reduction in the incidence and severity of the disease led to significantly higher grain yield of 1.09 t/ha in the treated crops compared to 0.67 t/ha in the untreated crops. Similarly, significantly higher straw or stover yield of 5.18 t/ha was recorded in the treated crops compared to 3.09 t/ha in the untreated crops. Three sprays with emulsified neem seed oil also gave higher grain yield (1.10 t/ha) and stover weight (4.61 t/ha) compared to one spray (0.75 t/ha and 4.05 t/ha, respectively) and the untreated crops (0.74 t/ha and 3.57 t/ha, respectively). Apron Star 42WS which is the latest formulation of metalaxyl as seed treatment in combination with foliar spray of emulsified neem seed oil gave adequate control of anthracnose and increased grain and stover yields of sorghum in the Sudan savanna of Nigeria.

The effects of cropping history on grain sorghum yields and anthracnose severity in Arkansas

Sorghum anthracnose, caused by Colletotrichum sublineolum , is found in most grain sorghum producing areas in the U.S.A., including Arkansas. High incidences and severities of anthracnose are infrequent and often limited to portions of some Arkansas fields. However, sporadic epidemics have occurred over many hectares and grain yield losses have been severe on susceptible sorghum hybrids suggesting that better management strategies are needed to improve and maintain high sorghum yields. The objective of this research was to evaluate the effect of previous cropping history on grain sorghum yields and on the severity of sorghum anthracnose in several agricultural environments in Arkansas. Replicated field experiments were conducted in 2005 and 2006 to evaluate sorghum following sorghum, sorghum following maize, sorghum following soybeans, and sorghum following rice on grain yields and anthracnose severity for 30 sorghum hybrids in 2005 and ten hybrids in 2006. The results show that the severity of anthracnose ranged from 0% to >23% and planting sorghum in fields one year after maize, soybeans, or rice appeared to significantly reduce the severity of sorghum anthracnose on most of the sorghum hybrids evaluated in both years. Although anthracnose severity varied across years in these experiments, the data show significant yield increases for most of the sorghum hybrids when sorghum was planted after rice, soybeans or maize, but not when sorghum was planted in the same field in which sorghum was grown in the previous year. Grain yields ranged from 0 kg ha −1 to more than 9500 kg ha −1 . These results demonstrate that planting sorghum after sorghum significantly increases anthracnose on most hybrids, that planting sorghum after rice, maize or soybeans can successfully reduce sorghum anthracnose, and that the economic benefits (yields) of these cropping sequences are partially dependent upon the year, the severity of the disease and the hybrid. Other management strategies such as sanitation, elimination of alternative hosts and planting clean, healthy seed or seed treated with an appropriate fungicide, coupled with disease resistance should be helpful and perhaps sufficient to avoid or reduce serious losses from grain sorghum anthracnose.

Temporal and Spatial Development of Sorghum Anthracnose in Arkansas

Development of sorghum anthracnose in time and space on susceptible ('BTx623' and 'Pioneer 8313') and resistant ('Cargill 888Y') sorghum (Sorghum bicolor) cultivars was investigated in field plots inoculated with a mixture of three strains (T430-SW, Ar54-SW, and ArSS-1SW) of Colletotrichum sublineolum in 2001 and 2002. After slow development during early growth stages, sorghum anthracnose developed rapidly after flowering. The logistic model provided a good statistical fit for disease progress curves for sorghum anthracnose in Arkansas. Compared to susceptible cultivars, the resistant cultivar had significantly lower values for the standard area under the disease progress curve, a lower upper asymptote, and delayed epidemic onset. However, there were no significant differences in infection rate and the time of the inflection points, the times at which the disease proportion equaled values of one-half of upper asymptotes, among the three cultivars. The negative exponential model more closely described disease gradients of sorghum anthracnose than the inverse power law model. There were significant differences in intercepts but not in slopes and half-distance between the resistant and susceptible cultivars. The slopes of disease gradients were significantly lower at 78 days after inoculation (DAI) than at 57 DAI on the three cultivars. The results could provide epidemiological components of sorghum anthracnose to help evaluate sorghum cultivars and breeding lines under field conditions.

Morphogenetic characterization of Colletotrichum sublineolum strains, causal agent of anthracnose of Sorghum

Anthracnose, caused by Colletotrichum sublineolum, has been one of the most destructive diseases affecting sorghum crops in Brazil. This study aimed to characterize wild and mutant strains through morphological and cultural characteristics, conidiation, and mating-type. A high variability was observed among strains when evaluated through radial growth and type of conidia produced. Spontaneous release of sectors by some strains was also observed, confirming the high genetic instability of this pathogen. Mating type genes amplified through PCRs using the primers, SKCM1, NcHMG and HGMgram demonstrated that both idiomorphs are present in this species. All the strains analyzed were self-sterile. It was not possible to correlate the auxotrophic mutant phenotype with the morphological characteristics evaluated.